It is known that rubber modified poly(alkenyl aromatic) resins are useful thermoplastic materials having a wide range of applications. Such resins because of their relatively low cost have become widely used commodities in spite of some deficiencies in impact strength, thermal resistance and surface appearance, e.g., gloss in thermoformed articles.
One of the more important modifiers for improving properties of rubber modified poly(alkenyl aromatic) resin compositions is a saturated rubber known as Kraton G, available from Shell Chemical Company. Kraton G is a saturated triblock copolymer styrene-butadiene-styrene or styrene-ethylenebutylene-styrene (SEBS rubber). These modifiers provide useful impact strength improvements as well as superior thermal aging performance. The latter property is especially important in rubber modified poly(alkenyl aromatic) resin compositions designed for medium to high heat requirement applications. Such superior performance, however, has been achieved at relatively great expense compared to conventionally available impact modification systems and many manufacturers have sought to improve the properties of rubber modified poly(alkenyl aromatic) resin compositions with other impact modifier candidates.
Yu et al., U.S. Pat. No. 3,944,631, discloses the modifications of styrene-acrylonitrile copolymers by adding an effective amount of an additive comprising a cross-linked (meth)acrylate rubbery core and a cross-linked interpenetrating styrene-acrylonitrile resin shell. The modifier is said to improve both impact strength and weather resistance in articles molded therefrom.
In the copending, commonly assigned application of Bates, Ting and Haaf, Ser. No. 837,406, filed Mar. 07, 1986, now U.S. Pat. No. 4,705,428, there are disclosed compositions comprising the core-shell modifiers of Yu et al. in polyphenylene ether resins, alone, or in further combination with rubber modified poly(alkenyl aromatic) resins.
It has now been discovered that useful rubber modified polyalkenyl aromatic compounds can be provided which exhibit vastly improved impact strength combined with thermal stability and high gloss while other physical properties such as Heat Distortion Temperature (HDT) are unchanged or only slightly affected, such as flow and tensile strength. These improvements are achieved by combining the base resin with a modifying compound comprising the aforementioned core-shell modifier of Yu et al. The cross-linked core-shell modifier appears to improve the properties of the rubber modified poly(alkenyl aromatic) resin without suffering from the thermal degradation often experienced following the use of conventional modifiers of the unsaturated, i.e., non-hydrogenated type.